Relational databases are the predominant method for storing repetitive data in computers because they allow efficient and flexible storage of that data. While medical directors and underwriters are more likely to use a spreadsheet than a database program to analyze their business, the data they wish to study are often stored in corporate databases. Or the data may be complex enough to require being keyed into or downloaded into a personal computer (PC) database program for storage, even if the data are then output to a spread-sheet for numerical analysis. In many circumstances, one can benefit from an understanding of efficient database design. After a brief overview, the reader is led step-by-step through a practical explanation of database design, from a flat file to a relational model.